Method of making contact point coating for relay contacts

ABSTRACT

A METHOD OF PRODUCING THE CONTACT POINT COATING FOR A RELAY CONTACT OF ONE TYPE WHEREIN THE CONTACT IS MADE OF AN IRON-NICKEL ALLOY, E.G. AS USED IN REED AND SIMILAR TYPE RELAYS. A LAYER OF GOLD IS INITIALLY APPLIED TO THE CONTACT POINT OF THE CONTACT AND THE CONTACT IS THEN TEMPERED AT A TEMPERATURE BETWEEN 700 AND 1000*C. THEREAFTER, A LAYER OF A TWO-COMPONENT ALLOY CONSISTING ESSENTIALLY OF GOLD   AND EITHER COBALT, NICKEL OR CHROMIUM IS DEPOSITED ON THE GOLD LAYER EITHER GALVANICALLY OR BY CATHODE SPUTTERING. FINALLY THE COATING MAY BE THERMALLY HARDENED BY A SHORT TIME FURTHER TEMPERING AT APPROXIMATELY 800*C. PREFERABLY IN A REDUCING ATMOSPHERE.

Jan'. 16, 1973 M. SCHIEKEL AL 3,711,383

METHOD OF MAKING CONTACT POINT COATING FOR RELAY CONTACTS Filed Aug. 27, 1971 United States Patent O g i 3,711,383 METHOD OF MAKING CONTACT POINT` COATING FORRELAY CONTACTS Manfred Schiekel, Helmut Sussenbach, and lngo Eichho Ulm (Da e), G any, ss r o: L ia Patent- Verwaltungs-GmbH, Frankfurt am Main, Ger -t many Filed Aug. 27, 1971, Ser. No. 175 ,6 2. Claims priority, application Germany, Aug. 28, 1970,

P 20 42 700. 3-33 Int. Cl. C03b /50; 5/52 U.S. Cl. 204-29'` 4' Clams ABSTRACT OF THE DISCLOSURE- BACKGROUND OF THE INVENTION,

The present invention relatesto a method for producing the coating for the contact points of relay contacts which are used` for example in reedor similar relays, and the resulting relay contacts.

A relatively large number of*relays with contacts enclosed in an air-tighthousing operate according tothe principles of reed relay developed by Bell Telephone Laboratories or very similar principles. A common characteristic feature of all of these relays is the common guiding of the magnetic and electrical flux through the contact point of the contact. The basic material for the contacting and magnetcally conductive parts of such relays is generally an iron-nickel alloy of identcal proportions by weight. Due to the maximum permeability m of this alloy being approximatcly 5 the magneticsconductivity thereof is suited for producng sufiiciently large magnetic adhesive forces. However, the electrical properties of these alloys, i.e. the high specific resitance of 70 mmP/m., the high contact resistance connecteditherewith and the unsatisfactory burnup properties; have made necessary the refinement of the contact giving regions or contact points and their surroundings in order to provide relays of this type which are useful for practical applications. That is, the metal at the contact points is altered or refined so that the contact points have neither high electrical nor high magnetic resistances.

The usual manner of contact refinement presently employed for this purpose is by means of the diffusion of gold. According to this process, a layer of fine gold of several micrometers thickness is deposited on the contact point of the nickel-iron basic contact material, and the gold is then diifused in a ditfusion process at approximate-` ly 900 C. to a depth of 10-15 m. The material thus produced at the contact point is a gold-nickel-iron alloy whose concentration ratio is determined by the quantity of the gold, the temperature, and the diffusion time. These alloys are suited as contact materials but they do not rep resent the optimum possible for the contact material since the technical expenditures involved for producing same are very high.

Batnted; Jan. 16, 1973 .cje-

Several sources have described contact materials on a gold base which are two-component alloys of gold and nickel, cobalt orchromium. Gold-alloy contacts for reed relays are for-eg. described in the periodical- Elektro Anzeiger, No. 15,' Aug. 9, 1967, pages 9-13'.

The experiments conducted by these sources have shown different travel behaviorfor anumber of types of' stresses (switching currents, switching voltageand inductance of the circut for-thel'various alloys). With a variation ofthe inductance in thecircuit to beswitched, a range was found in whichthe material moved=from theianode to the cathode at the same speed as in the opposite direction; i.e. the' total moveiient of materialin this case is-zero; This excellent moveirejnt` of material -can always be obtained fordiiferent inductances with different nickel; cobalt or chromum` concentrations in the contact allo-y. For gold and'nckel such alloys are known to contain up to 17% byweight of nickel.

SUMMARY: OF THE INVENTI Basedonttheknowledgeof these sources it is the object of; the presentinvention:to ,provide a mcthodefor producing contactopoin't coatings on relay contacts oftheabove mentioned type` with-. which itis possible to apply the aboveementione'd two-Component alloys ontothe contact points since this cannot be achieved wththeconventional diflusion method;

According tothe method' of: the present` invention, a goldlayer ist initiallyappliedto thecontact points; the contacts are thentempered ata temperature between 700 and, lOOO C.; andfinally, a two-componentalloysofa gold and cobalt, or gold and nickel,- or goldandchromium, is deposited onth e contact pointcther galvanica lly or by a de pu t r According to afurther feature of theinvention a de-. siredthermal hardening; of, the contact coating material can thenbe accpmplshed by a shortfurther tempering of the contacts at ;apprpximately 800 C. advsably in a re ducing, protective gas atmosphere. i

Examinations' with the X-ray microprobe have shown that at these teinperatures no noticeable diffusion of the gold alloy into the basc contact material takes place because of the low solubility of the contact point material or coating in the nickel-iron basic material. The rediffusion of the iron or nickel into the contact point material is so slight that no noticeable changes in the contact properties result.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to- FIG. 1 there is shown a reed relay including a glass vial or tube 1 having two switch or relay contacts 2 and 3 which were fused into the frontal faces 4 and 5 respectively of the glass vial 1. As is conventional in such relays, the contacts 2 and 3 are formed essentially of a ferromagnetic material. Preferably, in order to achieve proper bonding to the glass vial and to provide proper magnetic properties, the contacts 2 and 3 are formed of a nickel-iron alloy of equal proportions by weight, i.e., a mixng ratio of 50:50. Each of the contacts 2 and 3 is provided at its contact point, which is at the free end thereof, with a multilayer coating, 6 or 7 respectively according to the nvention, which has neither a high electrical resistance or a high magnetic resstance.

lt As 'shown in FIGZ the' contact pain coa ng 'tor' the contact comprisesa thi-n -layeaofn-goldv-s .which. is ap:

plied directly to the surface of the nickel-iron alloy contact 2 and an overlying layer `9 of a two-component alloy of -gold and nickel,-cob`a1t 'or chromium. I- he coatings 6 and 'l may only be applied to the adjacent p tQr ofithe .surfaces of the contacts 2 and 3,'or\may cover. the entire freeends `thereofif desired.j v- .1 a in According tO'the methOdofth invention the contact point coatings are produced initiallyapplyin:g tlierthin layer, e;g. 0.5 to 10 urn; thiclgof gold8 totheportion 'of the surface o-f contact 2 which isto serve as theicontact point with 'the other contact 3. The.applicationofi this gold layer 8 may begcarred out by any cgnventionally known process, e .g. ele ctrolytical ly. .The contact 2 with the gold layers is then temperedhy heating to a temperature ;betwe en 700 and 1000 VC. andthencooled;

P -900 i C-After coolingasecond layer-of about 2 thickness is galvanically deposited on this tempered gold layer. The second layer consists for example of a gold-cobalt alloy having about 5 percent cobalt. Preferably it is desired to harden this layer by means of a further temperng process The= t in e range for temperingmaybenlj to 9 O minutes.

The tempering process is carried; out;in an ;atmosphere free of oxygen, e. g. i n a dry nitrogen-.atmosphere.

j After cooling, tl e layer 9 forrnecl` from, a tw compw nent alloy consisting of gold and a metal s'electedrpm the group consisting of cobalt,ni ckel .and ch romium is de posited on the 'exposed' surface of gold" layer' 8 by conventional. galvanic or *cathode putterng techiijues'. If

galv'anic deposition is ntilized, the depositionoccursiri-:a`

mixture bath in whichgthe componentsrto be-zdeposited, i.e., gold and eithercobalt, nickel ora chromium,- 'are contained. The two-Component alloylayer hasa'prefer-red thicknessof about-0.2 to Sum; x u .r Afteridepositon of the two-componentalloyv layerl'9, a desirable thermalhardenin'g of the contact and contact point coating is thenpreferably' carried out byia short furthertempering of the contactat a temperature of approximately 800' C. This further preheating is preferably carred out in a' reducng, protective gas atmosphe're," eig a'nit''ogn-hydrogerrgas atmosphere: At a' temperatur-"of 800 C., a tempering time of approximately twoto'fiv 'minutes is sufficient. e

g 'According to a prefe-rd methd" of'th'e inyention the nickel-iron contact spring is covered on its ;contact range g alvanically With a gold layerjof about" 4 juinl and tern- It Will 'beurderstood that the above. description of the present-a inyention is susceptible to -various modifications, changes and`*adaptio'n s',:. and the same are intended to be cmprehe'hde'd* within' the meaning 'and `'range of equivalents of the appenclcl clairns.

point of a relay contact'suchiasare used in reed or similar -relays wherein the relay contact is formed of an ironnickel alloy, comprising: applying alayerof gold on the contact point; tempe'ing the contact at a temperature bei tween 700 and lOOO C.'; and thereafter depositing a layer of a two-component alloy consisting tessentially of gold anda rn'aterial 'se'lectedfrom thegroup consisting of coha1t;'nickel and' chromium, on the gold layer. a

The method dfined in claim lwherein said layer H ofa` two-Component 'allo-'y is deposited galvanically.

3. The' method defined `iri claim 1 wherein said layer Offa two-component alloy is' deposited by cathode sputtering. 

